More specifically, the invention concerns a method in which plutonium is separated from uranium and fission products by using an organic solvent including at least one crown compound.
For several years, the most widely used technique for carrying out the reprocessing of irradiated nuclear fuels consists of dissolving the fuel in a nitric solution, of then placing the aqueous nitric solution obtained in contact with an organic solvent so as to extract from the latter uranium and plutonium and separate them from most of the fission products, of re-extracting the uranium and the plutonium in an aqueous phase and of separating the uranium and the plutonium present in this aqueous phase by using an organic solvent. The organic solvent used most frequently is tributyl phosphate.
Although this solvent provides extremely satisfactory results, it does have the drawback of having insufficient resistance to radiations as it deteriorates via radiolysis in certain products, such as dibutylphosphoric acid, which adversely affect extraction. Moreover, when uranium is separated from plutonium by using this solvent, it is necessary to firstly carry out a stage for reducing the plutonium so as to keep the latter in an aqueous solution and extract the uranium (VI) from the tributyl phosphate. This requires additional stages and the introduction of reducing agents and stabilizers which adversely affect the subsequent processing.
Also, a large number of tests has been conducted on other solvents able to be used so as to overcome these drawbacks.
From those solvents able to be used, crown compounds have been selected as being most suitable as they have an improved affinity for plutonium than tributyl phosphate, they make it possible to separate uranium from plutonium without it being necessary to reduce the plutonium, and also they are more resistant when subjected to irradiation than tributyl phosphate, this crown compound remaining unchanged after irradiation for 140 hrs at a dose rate of 120 krad/hr.